Example of using NtOpenProcess and NtReadVirtualMemory

#include <Windows.h>
#include <iostream>

typedef struct _UNICODE_STRING {
	USHORT Length;
	USHORT MaximumLength;
	PWCH   Buffer;
} UNICODE_STRING, *PUNICODE_STRING;

typedef struct _OBJECT_ATTRIBUTES {
	ULONG           Length;
	HANDLE          RootDirectory;
	PUNICODE_STRING ObjectName;
	ULONG           Attributes;
	PVOID           SecurityDescriptor;
	PVOID           SecurityQualityOfService;
}  OBJECT_ATTRIBUTES, *POBJECT_ATTRIBUTES;

typedef struct _CLIENT_ID
{
	PVOID UniqueProcess;
	PVOID UniqueThread;
} CLIENT_ID, *PCLIENT_ID;

#define InitOA(ptr, root, attrib, name, desc, qos) { (ptr)->Length = sizeof(OBJECT_ATTRIBUTES);  (ptr)->RootDirectory = root; (ptr)->Attributes = attrib; (ptr)->ObjectName = name; (ptr)->SecurityDescriptor = desc; (ptr)->SecurityQualityOfService = qos; }
typedef NTSYSAPI NTSTATUS(NTAPI * __ntOpenProcess)(
	PHANDLE            ProcessHandle,
	ACCESS_MASK        DesiredAccess,
	POBJECT_ATTRIBUTES ObjectAttributes,
	PCLIENT_ID         ClientId
	);

typedef NTSYSAPI NTSTATUS(NTAPI * __ntReadVirtualMemory)(
	HANDLE ProcessHandle,
	PVOID BaseAddress,
	PVOID Buffer,
	ULONG NumberOfBytesToRead,
	PULONG NumberOfBytesReaded
	);

HANDLE get_handle()
{
	auto hWindow = FindWindowA(NULL, "window"); // find window of application

	if (hWindow == NULL)
		return INVALID_HANDLE_VALUE;

	CLIENT_ID uPid = { NULL };
	GetWindowThreadProcessId(hWindow, ( PDWORD )&uPid.UniqueProcess); // Get pid from window handle

	auto ntDll = LoadLibraryA("ntdll"); // load ntdll (windows nt functions)

	if (ntDll == NULL)
		return INVALID_HANDLE_VALUE;

	auto openProc = (__ntOpenProcess)GetProcAddress(ntDll, "NtOpenProcess"); // get ntopenproc

	if (openProc == NULL)
		return INVALID_HANDLE_VALUE;

	OBJECT_ATTRIBUTES attribs;
	InitOA(&attribs, NULL, NULL, NULL, NULL, NULL);

	HANDLE hProc = INVALID_HANDLE_VALUE;
	auto _openStatus = openProc(&hProc, PROCESS_ALL_ACCESS, &attribs, &uPid); // open it now
	SetLastError(_openStatus); // set last error for correct debugging, otherwise getlasterror will be 0x0

	return hProc;
}

int main()
{
	printf("Trying to open handle..\n");
	auto hProc = get_handle();

	if (hProc != INVALID_HANDLE_VALUE)
		printf("Opened handle at: 0x%X\n", hProc);
	else
		printf("Unable to open handle, Error Code: 0x%X\n", GetLastError());

	auto hModule = LoadLibraryA("ntdll");
	auto RVM = (__ntReadVirtualMemory)GetProcAddress(hModule, "NtReadVirtualMemory");

	if (RVM != NULL)
		printf("Could get NtReadVirtualMemory successfully\n");
	else
		printf("Couldn't get NtReadVirtualMemory, Error Code: 0x%X\n", GetLastError());

	// usage: auto testRead = RVM(hProc, address, &buffer, sizeof(whatever), NULL);

	getchar();
    return 0;
}